fs: remove useless lockdep assertion

mnt_ns_release() can run asynchronously via call_rcu() so hitting that
lockdep assertion means someone else already grabbed the
mnt_ns_tree_lock and causes a false positive. That assertion has likely
always been wrong. call_rcu() just makes it more likely to hit.

Link: https://lore.kernel.org/r/Z2PlT5rcRTIhCpft@ly-workstation
Link: https://lore.kernel.org/r/20241219-darben-quietschen-b6e1d80327bb@brauner
Reported-by: Lai, Yi <yi1.lai@linux.intel.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: brauner

fs/namespace.c

@@ -160,8 +160,6 @@ static void mnt_ns_tree_add(struct mnt_namespace *ns)
 
 static void mnt_ns_release(struct mnt_namespace *ns)
 {
-	lockdep_assert_not_held(&mnt_ns_tree_lock.lock);
-
 	/* keep alive for {list,stat}mount() */
 	if (refcount_dec_and_test(&ns->passive)) {
 		put_user_ns(ns->user_ns);